The present invention relates to concrete construction and more particularly to precast concrete structural units.
Concrete as a construction material has a long and interesting history. Although concrete is often thought of as being of recent origin, its history actually dates back to the early Romans who used a crude form of concrete in construction of the aqueducts. Steel reinforced concrete was in use during the 19th century. The first documented modern use of precast concrete was in the cathedral Notre Dame du Haut which was constructed in France in 1923. In that instance the precast concrete structural units were screen walls.
Precast, concrete structural units have been used in a wide variety of environments. Perhaps the earliest use of such precast units was a screen to provide a certain degree of privacy. Precast wall panels for use in buildings have been provided which carry no loads other than perhaps the force exerted by wind. Such precast wall panels typically have a height equivalent to the floor-to-floor dimension of the building in which they are incorporated. Precast wall panels, in a wide variety of sizes, shapes and finishes have been used.
Precast wall panels have also been used as load bearing units. Reinforcement, particularly with steel, becomes a major importance when precast wall panels are so used. Precast wall panels may also be used as wall supporting units, formwork and as shear walls extending over a plurality of floors or levels in a building. Various other precast concrete structural units have been known such as street furniture, planters, lighting standards, ornamental work, art and sculpture.
Precast concrete structural units have certain significant advantages over other structural materials. Perhaps one of the more important is that of providing a wide range of design expression in architecture. The quality control of precast concrete can be closely controlled thus providing material often superior in quality to poured concrete.
Precast concrete structural units generally are prepared by pouring wet mix concrete into suitably-shaped, reusable mold forms. The mold forms typically are made of steel and may be one piece molds or multi-piece molds, the latter being disassembled for removal of the poured concrete panel.
In the past some structural units have been provided with decorative surfaces. Perhaps the most prevalent decorative surface is provided by preparing the concrete utilizing a white sand resulting in a finished product which is very light in color. Other surfacing has been provided by washing away a portion of the concrete leaving exposed aggregate.